The FBI and local law enforcement were investigating a potential threat against a public transit system in the Los Angeles area on Monday.

The plot, according to police, targeted the Metro subway station in Universal City, about 10 miles northwest of Los Angeles.

Federal officials said they received information about the threat from an anonymous caller who contacted a public-safety hotline from overseas.

Officials did not specify where the call originated, but said the threat was communicated in English.

“We receive threats all the time, but this one was very specific with regard to date and location and for that reason we felt that it was important to provide some detail,” FBI Los Angeles spokeswoman Laura Eimiller told Business Insider Monday night. “This was to be a terrorist attack involving some sort of a detonation,” she said.

Information about who could be behind the threat has not yet been determined, Eimiller said.

In a press conference Monday, FBI officials and Los Angeles police said they were working to verify the veracity of the threat.

During a news conference on Monday, Los Angeles Mayor Eric Garcetti said he does not believe the threat is credible, “but with an abundance of caution, we always want to make sure that we protect our people here in Los Angeles.” He added: “My advice is right now, everyone should go about their normal day.”

City officials said there would be additional law-enforcement patrols at subway stations on Tuesday.